Here are this week’s gardening questions and answers, provided by Parker County Master Gardeners. To submit a question, send it to firstname.lastname@example.org. For more information about Parker County Master Gardeners, or to become a member, call 817-598-6096 or visit www.pcmg-texas.org.
Why is my grass not green? I fertilized according to directions, but it is a yellow-green.
You may have an iron deficiency. Parker County soils are notoriously high in phosphorous. Combined with our alkaline pH, phosphorus ties up the iron and does not let plants take in this nutrient. This symptom is known as iron chlorosis and it also affects some shrubs. You can apply iron sulfate (e.g., copperas) according to directions to help alleviate this problem. You should also choose fertilizers with little or no phosphorus.
My St. Augustine grass is coming out, but some of the leaves have a yellow appearance while others look fine. What should I do?
You may have St. Augustine Decline (SAD), which is a virus that weakens the plant and makes it more vulnerable to other diseases and insect damage. Early stages of SAD are often confused with iron chlorosis, but you can distinguish between the two. Leaves showing iron chlorosis are either uniformly yellow or have yellow stripes parallel to the main vein of the leaf. Leaves infected with SAD have more of a smudged or mottled appearance. The picture demonstrates this difference. The leaf on the left is affected by SAD and the leaf on the right by iron chlorosis.
While iron chlorosis can be corrected with applications of iron sulfate, there are no chemical controls for SAD. If your grass continues to lose vigor despite applications of fertilizer and iron sulfate, the best solution is to replace the diseased areas with a resistant variety such as Floratam, Floralawn, Raleigh or Seville. All are SAD-resistant varieties which will choke out the diseased grass over a period of years.